1. Field of the Invention
This invention relates to thermoplastic molding compositions based on fiber-reinforced polyethylene terephthalate compositions, and more particularly to fiber-reinforced blends of polyethylene terephthalate and selected copolyether-esters which give molded articles having reduced surface roughness.
2. The Prior Art
Glass fiber-reinforced polyethylene terephthalate has a number of advantageous properties as an engineering plastic. These include excellent dimensional stability, high strength and stiffness, and good physical characteristics. However, a major disadvantage of this material is that injection-molded articles tend to have very rough surfaces.
French Pat. No. 2,194,741 (equivalent to German Offen. 2,338,615) broadly discloses compositions containing polymer blends of a polyester with 1.5-90% of a poly(ether-ester) which contains 7-95% by weight of long-chain ester segments. Addition of the poly(ether-ester) gives molding compositions with improved impact strength. Although the patent mentions the addition of reinforcing materials such as glass fibers and filler, it does not exemplify fiber-reinforced polyethylene terephthalate resins, or mention the roughness problem associated therewith. In the only example illustrating the use of a filler (Example 7), polyethylene terephthalate was not used as the polyester. In the examples which employ polyethylene terephthalate as the polyester component (Examples 1, 4 and 8), the poly(ether-ester) component contains more than 60% by weight of long-chain ester segments.
In U.S. Pat. No. 3,652,713, polyester compositions with improved antistatic properties comprising a blend of polyethylene terephthalate with a polyether-polyester block copolymer are disclosed, but fiber-reinforced polymers are not disclosed. U.S. Pat. No. 3,652,714 teaches that the disperse dyeability and dry cleaning fastness of polyethylene terephthalate fibers are greatly improved by blending with a polyester-ether polymer such as polyethylene oxybenzoate.